A tooth can be implanted by inserting a dental implant into the jawbone (i.e., either the mandible or the maxilla), and by attaching a substitute or an artificial tooth to the dental implant. Generally, the dental implant is in form of an externally threaded screw, which is screwed into a pre-drilled bore of the jawbone, at an appropriate diameter. A major problem with dental implants is the dislodging of the dental implant, after a certain period of use, due to the forces which act on the dental implant during mastication.
Screw profiles and anchoring means directed to increase the bonding forces between the jawbone, and the dental implant, and to increase the life of the dental implant are known in the art. One such anchoring means utilizes grooves and holes in the body of the dental implant, to allow the osseous cells to grow into the grooves and the holes. Other anchoring means utilize screw threads of different pitches along the length of the anchoring means.
A major cause of dislodging of the anchoring means is insufficient bonding area. This problem is especially pronounced in the cancellous bone of the mandible and the maxilla, which is porous and therefore much weaker than the compact cortical bone. The cancellous bone is located beneath the cortical bone, and very often the anchoring forces which act between the dental implant and the cancellous bone are very small, thereby lending the bottom portion of the dental implant, which enters into the cancellous bone, literally useless.
U.S. Pat. No. 6,547,564 issued to Hansson, and entitled “Bone Implant Having Circumferentially Oriented Roughness”, is directed to a self tapping endosseous screw-type dental implant. The dental implant has an apical end, an intermediate section, and a coronal end. The apical end is presented by a first conical section. The coronal end is presented by a second conical section. The intermediate section is of a constant diameter, and extends from the apical end to the coronal end. The outer surface of the dental implant is provided with a screw threading which is divided into a coronal section and an apical section. The coronal section is positioned on the intermediate section. The apical section bridges the intermediate section and the first conical section.
The screw thread in the coronal section is in form of microthreads, having a height which is no greater than 0.2 mm, aligned parallel with one another at an inclined angle to the rotational axis. The screw thread in the apical section is in form of a macrothread, having a height greater than 0.2 mm, and in case of more than one macrothread, all macrothreads are also aligned parallel with one another, at an angle inclined to the rotational axis. The pitch of the screw thread of the apical section is the same as that of the coronal section. The quantity of the macrothreads in the apical section is less than that of the microthreads in the coronal section.
US Patent Application Publication No. 2005/0276676 A1, to Mardinger et al., and entitled “Orthopedic or Dental Device”, is directed to a dental device having a screw thread whose feature is variable along the length of the dental device. These features include the spacing between adjacent turns of the thread, the height of the thread, and the thickness of the thread. The feature can vary either continuously, or in an abrupt manner. A segment of the screw thread having widely spaced turns is meant to be inserted into a cancellous bone tissue, while another segment of the screw thread having narrowly spaced turns is meant to be inserted into compact bone tissue.
U.S. Pat. No. 6,030,162 issued to Huebner and entitled “Axial Tension Screw” is directed to a screw having a leading section, an intermediate section, a trailing section, and a self drilling tip. The screw thread of the leading section has a constant pitch. The screw thread of the trailing section has a constant but smaller pitch, and the screw thread of the intermediate section has a variable pitch connecting the leading section and the trailing section.
U.S. Pat. No. 5,427,527 issued to Niznick et al., and entitled “Dental Implant Method of Installation”, is directed to a cylindrical threaded implant. The implant has an angled abutment at a top portion thereof. The threads of the implant are interrupted by a plurality of closely spaced longitudinal channels, to provide a serrated appearance.